Papers by Keyword: Plasma Etching

Abstract: We studied the impact of plasma polish dry etch (PPDE) on SiC substrates and its effect on epilayers grown on PPDE treated substrates. PPDE treatment on chemo mechanical polished (CMP) surface shows no significant degradation in surface roughness even with 3µm removal. On the other hand, when a mechanical polished (MP) surface was treated by PPDE, surface roughness was improved, demonstrating that PPDE can smooth a rough surface post MP process. Selective etching of threading screw dislocations (TSD) was evident from pit formation on the substrate surface. These pits may generate extended structural defects (e.g. triangular defects) during the epilayer growth depending on the sizes of the pits. No evidence was found that PPDE selectively etched BPD in the substrate and, hence, no improvement in BPD conversion was seen after epilayer growth. Ideally, PPDE treated surface pits needed to be minimized at TSD sites and mild etching at BPD sites is preferable and subject to future optimization.

Abstract: Since SiC is hard and brittle, dicing by normal grinding process not only requires a long time for processing, but also reduces chip strength due to microcracks. The use of highly efficient and damage-free etching with high-pressure plasma as a chemical processing method for dicing rather than mechanical processing was investigated. The results of groove processing using a combination of a metal mask with slit-like apertures and plasma etching with high-pressure SF₆ plasma showed that the processing speed decreased with decreasing slit width and increasing groove depth. The results of electrostatic field calculations suggest that this is due to a decrease in plasma intensity caused by electric field decreasing.

Abstract: In addition to silicon carbide (SiC) and gallium nitride (GaN), gallium oxide (Ga₂O₃) is attracting attention as a widegap semiconductor material. Ga₂O₃, unlike SiC and GaN, is not as hard, but has strong cleavage properties, making highly effective mechanical machining difficult. Thus, the processing of Ga₂O₃ by high-speed etching employing atmospheric-pressure plasma was studied. An extremely high removal rate of 60 μm/min was obtained due to basic processing experiments using hydrogen gas instead of toxic and corrosive chlorine gas as the reaction gas.

Abstract: Microstructural analysis of commercially available cold-rolled polycrystalline copper foil, etched and annealed in an in-house developed Electron Cyclotron Resonance (ECR) Plasma Enhanced Chemical Vapour Deposition (PE-CVD) reactor, have been carried out using x-ray diffraction (XRD) studies. The annealing experiments were carried out under a vacuum environment, keeping the working pressure of the reactor at 50×10^-3 mbar, for three different time spans of 30 mins, 45 mins and 1 hour at 823 K (550 °C) and 923 K (650 °C) respectively in presence of hydrogen plasma. The XRD studies reveal the significance of annealing time at two different temperatures for the determination of physical and microstructural parameters such as the average grain size and micro-strain in copper lattice by Williamson-Hall (W-H) method.

Abstract: To reduce the on-resistance in vertical power transistors, backside thinning is required after device processing. However, it is difficult to thin silicon carbide (SiC) wafers with a high removal rate by conventional mechanical processing because their hardness and brittleness cause cracks and chips during thinning. Therefore, the authors have attempted to thin SiC wafers using plasma chemical vaporization machining (PCVM), which is plasma etching using high-pressure plasma. PCVM has a high removal rate because of the high radical density in the high-pressure plasma, and it does not form a damaged layer on the processed surface because of the low ion energy. The authors have already achieved a very high removal rate of 15.6 μm/min by PCVM. However, many etch pits were generated on the wafer during PCVM in these high-speed machining conditions. Therefore, this study, using molten potassium hydroxide (KOH) etching, investigated the cause of such etch pits and found that they may stem from threading screw dislocation in the wafers. In addition, this research considered a process for reducing an etch pit size and succeeded in doing so by controlling wafer temperature.

Abstract: Plasma chemical vaporization machining (PCVM) is an ultraprecise figuring technique for optical components without introducing the subsurface damage. In our previous study, the material removal volume was controlled by changing the scanning speed of the worktable. However, because of inertia of the worktable, a discrepancy between the theoretical scanning speed and the actual scanning speed will occur if the spatial change rate of speed is rapid. Therefore, we proposed the application of the pulse width modulation (PWM) control and the amplitude modulation (AM) control of the applied RF power to control the material removal rate (MRR). Experimental results showed that the relationship between the MRR and the average RF power had high linearity, the control range of the PWM control mode was from 0.19 x 10^-2 mm³/min to 3.90 x 10^-2 mm³/min (from 5% to 100%), which was much wider than that of the AM control mode.

Abstract: Silicon carbide (SiC) is a promising semiconductor material for high-temperature, high-frequency, high-power, and energy-saving applications. However, because of the hardness and chemical stability of SiC, few conventional machining methods can handle this material efficiently. A plasma chemical vaporization machining (PCVM) technique is an atmospheric-pressure plasma etching process. We previously proposed a novel style of PCVM dicing using slit apertures for plasma confinement, which in principle can achieve both a high removal rate and small kerf loss, and demonstration experiments were performed using a silicon wafer as a sample. In this research, some basic experiments were performed using 4H-SiC wafer as a sample, and a maximum removal rate of approximately 10 μm/min and a narrowest groove width of 25 μm were achieved. We also found that argon can be used for plasma generation instead of expensive helium gas.

Abstract: An anisotropic etching process for mesa structures using fluorinated plasma with hydrogen addition was developed in an electon cyclotron resonance setup. The evolution of the mesa morphology was studied in dependence on the gas composition, the applied bias and the pressure. The achieved side wall slope approached 90° with a negligible trenching. The aspect ratios of the fabricated structure in the developed residue free ECR plasma etching process were between 5 and 20.

Abstract: In recent years, silicon (Si) has been mainly used in power devices, but the limit of its performance is being reached. Therefore, silicon carbide (SiC) power devices have been attracting attention because they enable the fabrication of devices with low power consumption. To reduce the on-resistance in vertical power transistors, backside thinning is required after device processing. However, it is difficult to thin a SiC wafer with a high removal rate by conventional mechanical processing because its high hardness and brittleness cause cracking and chipping during thinning. Therefore, we have attempted to thin a SiC wafer using plasma chemical vaporization machining (PCVM), which is plasma etching using atmospheric-pressure plasma. In this study, we describe a machining property using a newly developed slit electrode that is composed of two parts and has a slit that allows for a new gas to pass.

Abstract: A one-dimensional fluid and Monte Carlo model is developed to study plasma sheath in dual ratio frequency plasma etching. Electrons and two positive ions are considerated. The influence of low frequency, ions mass diversity on IEDs and temperature uniformity of wafer is discussed. The results show that the IEDs are greatly modulated by the low frequency and ion mass, and the maximum and minimum ions energy can be predicted by using damped potential. The two ions with different ion mass affect each other little in IEDs but the total ion flux. The lower ion flux has higher averaged ion energy and the higher ion flux has lower averaged ion energy when keeping the total power fixed. It results in a similar temperature uniformity of wafer.